1. Field of the Invention
The invention relates in general to a leadframe, and more particularly to a leadframe for a multi-chip package and a manufacturing method for the same.
2. Description of the Related Art
Multi-chip package (MCP), a packaging technology attracting more and more attentions recently, integrates several chips of various types or passive pieces into a semiconductor package structure, so that the MCP achieves the features of more versatile functions or higher capacity. As the conductive path of the chips inside the package becomes more complicated, the commonly used chip carrier of multi-chip package is a multi-layer circuit substrate. In order to reduce the packaging cost, a low-cost leadframe is used to replace the multi-layer circuit substrate in a multi-chip package.
A leadframe for multi-chip package is disclosed in “Multi-chip IC Package”, Taiwanese Patent Publication No. 428875. The leadframe includes a die pad and a plurality of leads. A plurality of chips are attached on the die pad. A TAB tape is used to connect the soldering pad of the chips to the leads to overcome the difficulty encountered in cross-wire connection of the bonding wires. Currently, all of electrical connecting machines which use leadframe are wire-bonding machines, and applying TAB technology to leadframe involves the change in packaging equipment and bonding wires. Moreover, it is expensive and not practical to dispose a TAB tape on the current die pad or dispose an extra substrate.
Referring to FIG. 1, a most commonly used leadframe for multi-chip package is shown. A plurality of chips 30, 40, and 50 are disposed on a die pad 10 of a leadframe. A plurality of bonding wires 61, 62, 63, and 64 are used to electrically connect the chips 30, 40, and 50 to the corresponding lead 20 of the leadframe. The bonding wires 61 connect the chip 30 to the lead 20 positioned closer by. The bonding wires 62 connect the chip 40 to the lead 20 positioned closer by. The bonding wires 63 connect the chip 50 to the lead 20 positioned closer by. If the bonding wire is directly used to electrically connect the chip 50 to the lead 20 positioned farther away, the bonding wire has to cross over the chip 30 or 40. The bonding wire being too long is likely to be warded off during mold-pressing. Therefore part of the bonding wire 64 has to connect the chip 50 to the chip 30. A transferring circuit needs to be disposed on the active surface of the chip 30, and then connected to the chip 50 positioned farther away lead by other bonding wires 61. Therefore, the chip must have special design of circuits or dummy bonding pads, and cannot integrate multiple semi-conductor chips with ordinary circuit design into a die pad of a leadframe.